(1) Field of the invention
The present invention generally relates to an image forming apparatus such as a digital copy machine, and more particularly to an image forming apparatus in which a composite image obtained by composition of a plurality of images can be automatically formed.
(2) Description of related art
Conventionally, handling of confidential documents is an important matter for companies and public organization. Documents required for conventions are often copied in plural times and the copied papers are brought out. Thus, to keep a secret, serial numbers are previously provided on respective documents, and copies of the documents are distributed to persons participating in a convention. Then, relationships between persons to which the copies of the documents are distributed and serial numbers provided on the documents are recorded. Conventionally, an equipment for numbering documents when copying and an equipment for superposing a pattern (a serial number) on each of the documents when copying have been proposed.
However, when a document is copied in plural times with using the above equipments, a plurality of copied papers corresponding to the document have the same serial number. That is, numbers recorded on the copied papers corresponding to the document can not be changed one by one. Thus, in a case where the numbers recorded on the copied papers corresponding to one document are changed one by one, an operator must input to the equipment an instruction for changing the serial number to be recorded on each copied paper every copy operation of the document.
In addition, when the large number of documents are copied in plural times, a sorter unit is used to effectively perform the copy operations. To reduce the number of copied papers, a duplex copy in which images are formed on two sides of each of copied papers is performed. In these cases, also it is desired that serial numbers be effectively recorded on each copied paper.